JPH02216748A - Sample surface unevenness observation method by reflection electron beam diffraction - Google Patents

Abstract

PURPOSE:To detect the unevenness on the surface of a sample by the atomic layer level, by scanning the designated area of the sample surface with the electron beams, detecting the intensity of the diffraction electron beams at a time at plural points in which the intensity is varied inversely at the atomic layer steps existing at the opposite surface of a diffraction pattern, and carrying out an operation between the intensities of plural diffraction electron beams. CONSTITUTION:The diameter of the incident electron beam 4 generated from an electron gun 1 for diffracting the reflection electron beam of a reflection high speed electron beam diffraction device is focused in order to observe its minute area, and the surface of a sample 3 loaded in a vacuum chamber 28 is scanned. The electron beam 4 from the electron gun 1 is injected to the surface of the sample 3 at the incident angle theta, and diffraction electron beams 5 depending on the crystal orientation and the plainness of the atomic layer level of the surface are generated. The electron beams 5 are injected to a fluorescent plate 6 for reflection electron beam diffraction spot observation. The output of the fluorescent plate 6 is added to an operation circuit 13 through photo-fibers 7-9, an operation is applied to the intensities between the diffraction electron beams detected simultanously, and the unevenness of the sample surface is detected by the atomic layer level.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a method for observing an uneven structure on an atomic scale on a sample surface using reflected electron beam diffraction.

(Prior Art) As the performance of semiconductor devices increases, it has become necessary to control surface flatness at the atomic level. For example, when growing different materials on a substrate by heteroepitaxial growth,
Specifically, when depositing polar GaAs or the like on isotropic Si, it is desirable to line up monoatomic steps at appropriate intervals on the substrate surface in order to control polarity. When manufacturing a device, it is desirable that the substrate surface be as flat as possible at the atomic layer level, since surface irregularities cause a decrease in electron mobility.

At present, growth is performed on a substrate by molecular beam epitaxial growth (MBE) while monitoring changes in the diffraction intensity of reflection high-energy electron diffraction (RHEED) using an electron beam accelerated to about 10 kV to 30 kV. It has become possible to control the thickness of thin films at the atomic layer level. However, since conventional RHEED can only obtain average information on the entire surface, it is not possible to control the flatness at the atomic level of the surface corresponding to the IJj7 layer and below in the micro region where the device is manufactured.

Under these circumstances, a method to observe the flatness of the surface was researched, and the reflection electron microscopy method was developed, in which the transmission electron microscope WIi* is placed in an ultra-high vacuum and the sample is set so that the electron beam is incident on the surface so that it forms an image. (REM method), and the microprobe reflection high-speed electron diffraction method (μ-RHE
It was shown that it is possible to observe monoatomic layer steps on the sample surface by imaging the intensity change of a single diffraction spot using the ED method. However, with this method, the contrast of images of atomic layer steps is low (and since there is no means to specify the observation area, it is possible to obtain a concept of the distribution state of atomic steps on the entire sample surface, but step observation, flat No equipment has been developed that can observe the degree of radiation.

(Issues to be Solved by the Invention) The present invention solves the conventional problems as described above, and uses a reflection high-speed electron beam diffraction method that detects the diffraction of an electron beam incident on the sample surface. The aim is to enable the observation of flatness at the atomic level.

(Means for solving the problem) Scan a designated area on the sample surface with an electron beam converging on the sample surface, and in the diffraction pattern, the intensity changes in opposite directions at the atomic layer step portions existing on the sample surface. By simultaneously detecting the intensity of the diffracted electron beam at a plurality of points, and further performing arithmetic processing between the intensities of the plurality of diffracted electron beams, the unevenness of the sample surface can be detected at the atomic layer level.

(Function) In the present invention, diffraction occurs on the electron beam diffraction pattern when the electron beam irradiates a flat area on the sample surface with no atomic layer steps and when it irradiates the atomic layer step portion. Atomic layer steps are detected by simultaneously detecting the intensities of multiple diffracted electron beams by selecting multiple points where the intensity increases on one side and weakens on the other, and performs arithmetic processing on the results. Compared to detecting atomic layer steps only from changes in the intensity of diffraction spots, the flatness of the surface has much better contrast <11! It can be +111.

(Example) A reflection high-speed electron diffraction apparatus according to the present invention will be described below.

FIG. 1 shows a reflection high-speed electron diffraction apparatus according to the present invention.

In this example, only the part related to reflection high-speed electron beam diffraction is illustrated, but for example, it may be connected to a molecular beam epitaxy (MBE) apparatus via a gate valve, or the electron beam may be connected to a molecular beam epitaxy (MBE) apparatus through a gate valve. Equipment related to source and detection may be incorporated. Furthermore, the analysis device may be combined with a device capable of non-destructively analyzing surface components, such as an Auger electron spectrometer, a photoelectron spectrometer, or an X-ray microanalyzer. 1 is an electron gun for reflection electron beam diffraction (RHEED gun). In order to observe a minute area on the micron order, it is desirable that the diameter of the electron beam 4 formed by this electron gun be narrowed down to 0.1 μm or less, and the electron beam should be as close to parallel as possible (the opening angle of the beam is also approximately The acceleration voltage is preferably 10 to 50 kV, preferably approximately 20 kV. In this case, the wavelength of the electron beam is approximately 0.07 radians, and the incident angle θ to the sample 3 is , 1 ~
Since the angle is 5°, the electron beam penetrates only a few atomic layers from the surface. 6 is a fluorescent plate (detection surface) for measuring reflected electron beam diffraction spots IlI. A diffraction pattern is generally formed on the fluorescent screen 6 by the diffraction electron beam 5 caused by the electron beam 4 emitted from the RHEED gun 1. The signal from the diffraction spots is transmitted through the optical fiber? , 8.9 and photomultiplier 10
．． 11 and 12, and is calculated in the calculation circuit 13. The arithmetic circuit multiplies the intensity of each diffraction spot by an arbitrary constant, and performs addition/subtraction between the intensities of the multiplied diffraction spots.

The processed signal 14 is input to the CRT 15 as a luminance signal. A diffraction intensity image from above the sample surface (hereinafter referred to as a scanning RHEED image) is displayed on the CRT 15 in synchronization with the scanning signal 16 of the electron beam from the RHEED gun.

In this example, the fluorescent screen is made to emit light by a diffracted electron beam, and the intensity of the emitted light spot on the fluorescent screen is picked up by an optical fiber and guided to the photomultiplier tubes 10, 11, and 12. However, if the intensity of the diffracted electron beam can be detected, there is a method is not limited to the above method.

In this example, the number of optical fibers is three, but it is four.
It may be more than a book. Furthermore, the optical fiber can be placed outside a vacuum and moved mechanically to measure the intensity of the diffraction pattern at any position. The position where the optical fiber is installed may be at the diffraction spot itself or may be intentionally shifted from the position of the diffraction spot. 3 is a sample.

In this example, a sample with a diameter of 2 inches can be observed. The sample moving mechanism 30 can move the electron beam incident position 29 to any point on the entire surface of the 2-inch wafer. 25
is a vacuum exhaust facility. In this example, it is composed of an ion pump and a titanium sublimation pump.
The structure is not limited to the above, as long as it can be evacuated to a pressure of Xl0-' Pa or less and the vibration of the entire vacuum chamber 28 can be suppressed to about 0.1 μm or less. Reference numeral 27 denotes a sample exchange preliminary chamber, which prevents the vacuum chamber 28 from being exposed to the atmosphere (
This is to exchange samples.

An example of observation of an atomic layer step according to this example will be described below.

After loading the sample 3, the sample position is determined through the observation window 24. In general, nothing can be observed on the surface of the sample 30 where the lower step [1111 is performed] by observation using an optical microscope, etc., so it is desirable to specify the observation area using a marker intentionally formed on the sample surface. Examples of diffraction patterns and diffraction spots are shown in FIG. The same numbers as those in FIG. 1 are indicated by the same numbers. Incident electron beam 4 from RHEED gun 1
is incident on the surface of the sample 3 at an incident angle θ. The incident angle θ is approximately 1° to 3°. The incident electron beam 4 generates a diffracted electron beam 5 that depends on the crystal orientation of the sample surface and the flatness of the surface at the atomic layer level. When the flatness of the sample surface is less than a few tens of angstroms, a diffraction pattern 32 as shown in FIG. 2 is usually produced. In the conventional RHEED device, the incident electron beam 4 is detected using the intensity change of the diffraction spot (corresponding to point A on the diffraction pattern 32) at the intersection point of the zero-order Lauering on the line 35 perpendicular to the sagittal plane 31 and the detection plane 6. The scanning RHEED (I) was displayed on a CRT 15 by scanning the surface of the sample. In Fig. 2, S is a part that is one atomic layer high on the sample surface, and the area around this S is an atomic layer step. The intensity of the diffraction spots is
Because the change occurs in the atomic layer steps 33 and 34 on the sample surface, contrast occurs in the scanned RHEED image. However, with the intensity change of the only diffraction spot, the intensity change in the atomic layer step 33 and 34 is small. (It is not possible to obtain an atomic step image with strong contrast. For example, a scanning RHE with very poor contrast as shown in Figure 3 d)
Only the ED image can be viewed 1lfllll.

However, with the device according to the present invention, by using three fibers to simultaneously measure intensity changes at multiple locations on the diffraction pattern, and by performing mutual calculation processing, it is possible to It is possible to clearly detect and display the atomic layer step as shown in FIG. 3e.

For example, diffraction spots reflect the unevenness of the sample surface at the atomic layer level, and as shown in Figure 2B, the electron beam irradiation point becomes a spot in a flat area, but is not a clear spot in an atomic layer step area ( , it may form a vertically long streak-like shape. This is noticeable when the step is orthogonal to the incident electron beam due to the direction of the atomic layer step. In this example, the detection position of the diffraction spot by the optical fiber is shown in Fig. 2B. is shown.

The position where the diffraction spot appears (α point) and the slightly shifted position (β point)
The intensity change at point) was detected, and the following calculation was performed: 1÷1 (intensity at point α) - (intensity at point β) (The result was observed as a scanning RHEED image.

As a result, as shown in Figure 3a, a scanning RHEED image with strong contrast could be observed only in the atomic layer step portion.

Furthermore, as explained below, by using three simultaneous measurement points on the diffraction pattern and using arithmetic functions, it was possible to observe two-dimensional atomic layer steps on the sample surface with good contrast. In the observation example in Figure 3a, the sagittal plane 31 in Figure 2
By calculation between two points on the line 35 orthogonal to the detection surface 6,
Increased contrast of atomic layer steps.

Next, intensity calculation is performed between a diffraction spot on a line 35 perpendicular to the sagittal plane 31 and the detection plane 6 (for example, point A in FIG. 2A) and a diffraction spot on a line parallel to the perpendicular line 35 (for example, point 0). By doing so, as shown in FIG. 3, the contrast between the atomic layer step shown in FIG. 3a and the atomic layer step perpendicular to the sample surface can be increased. In other words, the above α, β
By calculating the intensities of the diffraction spots at three points , C, it was possible to detect and display the atomic layer step with high contrast, regardless of the direction of the atomic layer step, as shown in FIG. 3C. Atomic layer step Il! The atomic layer step can be observed even if the diffraction spot used in the above embodiment is not used, for example, by using a 0th-order Lauelling or a 1st-order Lauelling-like spot in FIG. 2.

At this time, the contrast of the atomic image step can be increased by calculating the difference in intensity changes between two or more points.

(Other Examples) In the example shown in FIG. 1, only the two-dimensional distribution of atomic layer steps on the surface of the sample 3 can be measured.

Before forming a thin film for semiconductor devices, it is necessary to control surface irregularities at the atomic layer level, but with the atomic layer step scanning RHEED image according to the present invention, the distribution of atomic image steps can be displayed in seconds. Dynamic changes in atomic image steps over time can be observed on the spot.

FIG. 4 shows the time of the current observation device. The same parts as in FIG. 1 are indicated by the same numbers. 45 is a holder that holds the sample 3; A heater made of Ta is placed on boron nitride, and sample 3 can be heated to a maximum of 1000°C. 43 is a light source for heating only the surface of the sample 3. As a light source, Xe lamp, W lamp, He-
Na laser, YAG laser, CO2 laser, etc. are used.

The light beam may be scanned across the wafer to heat the entire wafer. 41 is an ion gun for introducing etching gas. As ions, inert gas Ar, Xe,
In addition to Kr, fluorine gases.

Chlorine gas can be introduced. As shown in the embodiment shown in Fig. 3, the RH is equipped with a sample heating function and an etching function.
Using the EED device, we were able to observe how the atomic layer steps on the sample surface change due to heating and etching. FIG. 5 shows an example of changes in atomic layer steps due to heating. In the same figure, the movement of the steps due to heating can be seen clearly: before heating (a) and after heating (b).

(Effects of the Invention) According to the present invention, I! of the atomic layer step on the sample surface! The measurement is based on the change in the intensity of a single diffraction spot during scanning of the sample surface by the electron beam. Because of the detection, the atomic layer steps are detected and displayed very clearly.

[Brief explanation of the drawing]

Fig. 1 is a longitudinal cross-sectional side view of an apparatus according to an embodiment of the present invention, Fig. 2A
is a diagram of a diffraction pattern obtained by the above device, FIG. 2B is an explanatory diagram of the operation of the present invention, and FIG. 3 is an example of a display pattern according to the present invention.
FIG. 4 is a longitudinal sectional side view of another embodiment of the present invention, and FIG. 5 is a diagram showing an embodiment showing movement of atomic layer steps by heating. l...Reflected electron diffraction-like electron gun (RHEED) gun, 3
... Sample, 4... Electron beam from RHEED gun, 5.
... Backscattered electron diffraction line, 6... Fluorescent plate for backscattered electron diffraction spot observation (detection surface), 7... Optical fiber 1.8.
・・Optical fiber 2.9・・Optical fiber 3.10・
... Photomultiplier tube 1, 11 ... Photomultiplier tube 2.12
...Photomultiplier tube 3.13...Arithmetic circuit, 14...
・Electrical signal obtained from reflected electron beam diffraction spot intensity, 15
...CRTI, 16...Scanning signal for scanning the electron beam from the RHEED gun, 17...Electron beam from the SEM gun, 18...Secondary electrons emitted from the sample surface by the incident electron beam , 19... secondary electron detector, 20...
Secondary electron signal, 21...CRT2.22...RHE
Scanning signal for scanning the electron beam from the ED gun, 23.
...Scanning signal for scanning the electron beam from the SEM gun,
24... Sample observation window, 25... Vacuum exhaust equipment, 2
6...Gate valve, 27...Sample loading preliminary chamber, 2
8... Vacuum chamber, 29... Electron beam incidence point, 3
0... Sample movement mechanism, 31... Sagittal plane of incident electron beam, 32... Diffraction pattern, 33... Atomic layer step perpendicular to the sagittal plane, 34... Atomic layer parallel to the sagittal plane step. 41... Ion gun for introducing etching gas, 42... Ion beam, 43... Ion beam, 43... Sample surface heating light source, 44...
Light beam, 45...Sample holder with heater. Agent Patent Attorney Hiroshi Agata II Figure 2 (,4) Figure 2 (B) 111 Figure 13! ! 1 14 In Figure 1 (a (b) Figure 5 1, It) 71

Claims (1)

[Claims] A means for scanning the sample surface with an electron beam converging on the sample surface, and a diffraction pattern formed by the diffraction electron beam from the sample surface, in which the intensity of the diffracted electron beam is reversed at the atomic layer step of the sample surface. A method for observing irregularities on a sample surface using reflected electron beam diffraction, comprising means for detecting the intensity of a diffracted electron beam at a plurality of points showing a phase change, and a means for performing arithmetic processing on the outputs of the plurality of detection means. .